Where are located the nextcloud web user

Hello guys
quick question. where are the users or where are located the users (linux => passwd?) that we created in nextcloud?
lets say that I created the user joe, how can I link this user with a normal account in linux?
I would like to modify the permissions



The user has got a directory in …/nextcloud/data …
The user and password is in the database e.g. MariaDB

Use “occ”